The present invention relates to the field of catheters, and in particular to a catheter for nerve blocks in anesthesia.
In anesthesia, for lengthy operations, postoperative pain therapy, and treatment of chronic pain states, the nerves supplying a specific region of the body are often blocked by an anesthetic. A catheter is used to introduce the anesthetic, and the distal end of the catheter is positioned as close as possible to the nerve to achieve an optimum effect with a minimal quantity of anesthetic. The catheter, which can remain in position for a long time if necessary, includes a long, thin, flexible plastic tube.
To insert the catheter into the sheath or canal of the nerve, a cannula is used to insert the catheter. U.S. Pat. No. 5,007,902 teaches replacement of such a cannula by a puncture cannula, in which case the puncture cannula is pulled away in order to insert the catheter. German patent DE 3643235 C1 teaches a puncture cannula whose internal canal emerges at the side behind the distal tip of the cannula, with the catheter being inserted and positioned by means of this puncture cannula. Once the catheter is in position, the cannula used for its insertion is removed.
U.S. Pat. No. 5,007,902 also teaches the use of electrical nerve stimulation for precise positioning of the catheter. In this case, a guide wire is inserted in the catheter, and its distal end protrudes slightly from the distal end of the catheter. The proximal end of the guide wire is electrically contactable for connection of a stimulator. Using electrical simulation, the position of the distal end of the catheter can be determined exactly while the catheter is being inserted into the sheath or canal of the nerve. Since the guide wire completely fills the internal cross section of the catheter, the wire has to be removed from the catheter as soon as the catheter is in place in order to apply the anesthetic through the catheter. If the catheter remains in place for a long period of time and further medication has to be introduced, it is often necessary to check the position of the catheter and possibly correct it. It is necessary for this purpose to insert a guide wire once again to determine the position of the distal end of the catheter by electrical stimulation.
It is also known that a thin wire can be disposed in the catheter for electrical stimulation, the cross section of which is smaller than the free internal cross section of the catheter. In this way, the wire does not impede introduction of a liquid through the catheter so that the wire can remain in the catheter. The position of the wire, fixedly disposed in the catheter, can be checked by electrical stimulation and corrected for the entire time that it is in place. However, if the thin end of the wire protrudes from the distal end of the catheter, there is a risk that the tip of the wire may cause damage and injury to the nerves while the catheter is being pushed forward. If the wire does not protrude from the distal end of the catheter, although this risk is reduced the electrical contact for electrical stimulation is no longer reliably assured.
Therefore, there is a need for a catheter for a nerve block that can be positioned by electrical stimulation, ensuring a reliable contact for electrical stimulation and a minimal risk of injury, and making it possible for the catheter position to be checked at any time by electrical stimulation.